System and method for determining density of a medium in a tank

A system and method for determining a density of a non-conducting medium in a tank is disclosed where the relationship between a dielectric constant and a density of the medium is known. The system comprises a transceiver, and a waveguide, the waveguide extends towards and into the medium. The system further comprises a first microwave resonator located along the waveguide. The first microwave resonator has a resonance frequency, which depends on a dielectric constant of a medium surrounding the resonator according to a known relationship, and is arranged to reflect a portion in the frequency domain of a signal being guided along the waveguide. The system further comprises processing circuitry connected to the transceiver and configured to determine the resonance frequency based on a received reflected signal, and to determine a density of the medium at the location of the first microwave resonator based on the resonance frequency.